Washing/drying method utilizing sonication

ABSTRACT

A washing/drying method utilizing sonication, comprising: dipping a material to be washed into an aqueous solution containing a surfactant having a water repellency so that at least one molecular layer of the water repellent surfactant is attached to the surface of the material to be washed; applying sonication to the aqueous solution; and then drying the material according to a known drying method such as vacuum drying, shaking off, blowing with gas and heating; or heating the material to be washed with steam at a temperature of less than 100° C. in an atmosphere reduced to a pressure such that the boiling point of water becomes less than 100° C.; and then drying the material according to a known drying method such as vacuum drying, shaking off, blowing with air, and heating.

This application is a continuation of application Ser. No. 08/005,329,filed Jan. 15, 1993, now U.S. Pat. No. 5,361,789, which is a divisionalof application Ser. No. 07/691,915, filed Apr. 26, 1991, now U.S. Pat.No. 5,203,927.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a washing/drying method and awashing/drying apparatus suitable for a thorough washing and/or dryingof a material to be washed, such as precision electronic parts andprecision electronic device parts, which must be thoroughly washed inthe preparation steps thereof (i.e., thorough washing) and, from thestandpoint of production efficiency or corrosion resistance, in whichthe washing liquid after washing must be removed by drying within ashort time.

2. Description of the Related Art

In the prior art, the thorough washing in the preparation steps ofprecision parts and electronic device parts, where an attachment ofcontamination or dust can not be allowed, has been practiced primarilyby washing with a fluorocarbon.

As the detergent for such a thorough washing, other than a fluorocarbon,there is known a solvent of the chlorine type such as trichloroethylene,but in the case of a metal product, the chlorine liberated in thewashing step may be adhered and cause rusting, and in the case of aresin or rubber product, a deformation or dimensional change due toswelling may occur, and thus a problem arises of an adverse affect onthe product. In contrast, in the case of a fluorocarbon, no such problemarises and drying occurs within a very short time, and therefore,washing with Freon 113 (fluorocarbon manufactured Mitsui DupontFluorochemical Co. Ltd.) has been employed in the prior art.

A fluorocarbon is harmless to human beings and animals but destroys theozone layer, which has become a worldwide problem in recent years, andin the interest of environmental protection on a global scale thetendency is now toward completely abolishing the use of fluorocarbons.From such a standpoint, as an alternative to the washing method using afluorocarbon, the development of a washing water which will not needregulation in the future is now under way.

The critical point of thorough washing, in addition to a thoroughcleaning ability, is that the drying after washing can be carried outrapidly and thoroughly. Also, there should be no adverse affect on thematerial to be washed, as in the case of a detergent of the chlorinetype mentioned above.

When washed with water, it is necessary to prevent the precisionelectronic part, constituted of a metal from rusting. Since the boilingpoint of water is as high as 100° C., compared with that of Freon 113,which is 47° C., it is difficult to vaporize, and a part with acomplicated shape or a blind tap hole can not be dried within a shorttime and without difficulty.

SUMMARY OF THE INVENTION

Accordingly, the objects of the present invention are to eliminate theabove-mentioned disadvantages of the prior art and to efficientlyperform thorough washing and drying, after washing of the metallic ornon-metallic material to be washed, without an adverse influence on thematerial, by a method other than one using a fluorocarbon.

Other objects and advantages of the present invention will be apparentfrom the following description.

In accordance with the present invention, there is provided awashing/drying method, comprising; dipping a material to be washed intoan aqueous solution containing a surfactant having a water repellency sothat at least one molecular layer of the water repellent surfactant isattached to the surface of the material to be washed; and then dryingthe material.

In accordance with the present invention, there is also provided amethod of drying, after washing, comprising: dipping a material to bewashed into an aqueous solution containing a surfactant having a waterrepellency so that at least one molecular layer of the water repellentsurfactant is attached to the surface of the material to be washed;heating the material to be washed with steam at a temperature of lessthan 100° C., preferably 80° C. to 95° C., in an atmosphere reduced to apressure such that the boiling point of water becomes less than 100° C.,preferably 80° C. to 95° C.; and drying the material.

In accordance with the present invention, there is further provided amethod of drying after washing, comprising: placing a material to bewashed in a vacuum chamber; heating the material to be washed with steamat a temperature of less than 100° C., preferably 80° to 95° C., in anatmosphere reduced to a pressure such that the boiling point of water isless than 100° C., preferably 80° C. to 95° C., and subsequently blowinga gas onto the material and, thereafter, vacuum drying the material.

In accordance with the present invention, there is further provided amethod of drying after washing comprising: placing a material to bewashed in a vacuum chamber; heating the material to be washed with steamat a temperature of less than 100° C., preferably 80° C. to 95° C., inan atmosphere reduced to a pressure such that the boiling point of wateris less than 100° C., preferably 80° C. to 95° C.; subsequently blowingonto the material a gas, such as air; and thereafter, vacuum drying thematerial.

In accordance with the present invention, there is further provided awashing/drying apparatus having a water tank for receiving and holdingtherein an aqueous solution containing a surfactant having a waterrepellency, a shower washing device for removing superfluous surfactantattached to the material to be washed in said water tank, and a vacuumchamber for drying the material to be washed after shower washing. Thevacuum kettle has a means of jetting steam so that the material to bewashed can be heated with steam at a temperature of less than 100° C.,preferably 80° C. to 95° C., in an atmosphere reduced to a pressure suchthat the boiling point of water is less than 100° C., preferably 80° to95° C., and has a gas blowing means so that the water can be drained byblowing gas.

In accordance with the present invention, there is still furtherprovided a drying apparatus comprising: a device for irradiating amaterial to be washed with electromagnetic wave irradiation as a meansfor heating moisture adhered to the material, and at least one meansselected from the group consisting of: (i) a gas blowing means forblowing gas on the material to be washed to remove water; (ii) a meansfor evacuating or reducing pressure applied to the material so that themoisture adhered to the material is removed; and (iii) a means ofcentrifuging the material so that the subject is spun-dried throughcentrifugation, all during or after heating by the electromagneticwave-irradiation device.

In accordance with the present invention, there is still furtherprovided a foam-suppressing apparatus comprising: an overflow vesselreceiving an overflow from a washing vessel containing asurfactant-containing washing solution therein arranged in a washingcirculation system of a washing apparatus; and a valve means provided ata liquid outlet portion of the overflow vessel for controlling theliquid level of the overflow vessel such that air is not included in thewashing solution effluent from the overflow vessel.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be better understood from the description setforth below with reference to the accompanying drawings, in which:

FIG. 1 is a diagram illustrating the basic principles and steps of thewashing method and the method of drying after washing according to thepresent invention;

FIG. 2 is a drawing of the steps of, and a sectional view showing anexample of the apparatus for performing the washing and drying;

FIG. 3 is a drawing of the steps of, and a sectional view showing anexample of the apparatus which performs, a washing treatment accordingto the present invention, without using the aqueous solution of a waterrepellent surfactant;

FIG. 4 is a drawing showing the chain structure of a perfluoroalkylcarboxylate, which is one example of the water repellent surfactantaccording to the present invention, and a model in which the surfactantis adhered, as a one molecular layer, on the surface of the material tobe washed;

FIGS. 5A and 5B to 7A and 7B are respective, plan and side elevationalviews of other examples of the drying apparatus according to the presentinvention;

FIG. 8 is a drawing illustrating a conventional washing system using awashing solution containing a surfactant;

FIG. 9 is a drawing illustrating one example of a foam-suppressingdevice according to the present invention; and

FIGS. 10 to 20 are drawings illustrating other examples of thefoam-suppressing devices according to the present invention.

FIGS. 21 is a diagram illustrating the preferable steps of thewashing/drying method and apparatus according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is the diagram illustrating the basic principles and steps of thewashing method and the method of drying after washing.

According to the first embodiment (1) of one aspect of the presentinvention, when carrying out a washing/drying during the process ofpreparing parts or electronic parts, a material to be washed is dippedinto an aqueous solution containing a surfactant having a waterrepellency so that at least one molecular layer of the water repellentsurfactant is attached or adhered to the surface of the material to bewashed, followed by drying according to a known drying method such asvacuum drying, shaking off (e.g., centrifuging), gas (e.g., air)blowing, heating and others.

Since the aqueous solution of a water repellent surfactant also has awashing effect, washing also may be carried out by dipping the materialto be washed in an aqueous solution of a water repellent surfactant, orit is sufficient to dip the material, washed in another step, in anaqueous solution of a water repellent surfactant so that at least onemolecular layer of the water repellent surfactant is attached thereto.

Thus, after washing with an aqueous solution of a water repellentsurfactant, or by dipping the material washed in another step into anaqueous solution of a water repellent surfactant, at least a molecularlayer of the water repellent surfactant is attached to the surface ofthe material to be washed, before drying same according to a knowndrying method such as vacuum drying, shaking off, gas blowing, heatingand others.

According to the second embodiment (2) of the present invention, asdescribed above, after dipping a material to be washed into an aqueoussolution containing a surfactant having a water repellency so that atleast one molecular layer of the water repellent surfactant is attachedto the surface of the material to be washed, the material to be washedis heated with steam at a temperature of less than 100° C., preferably80° C. to 95° C., in an atmosphere reduced to a pressure at which theboiling point of water is less than 100° C., preferably 80° C., to 95°C., and then the material is dried by a known drying method such asvacuum drying, shaking off, gas blowing, heating and others.

According to the third embodiment (3) of the present invention, asdescribed above, a material to be washed is dipped into an aqueoussolution containing a surfactant having a water repellency so that atleast one molecular layer of the water repellent surfactant is attachedto the surface of the material to be washed, then the material to bewashed is heated with steam at a temperature of less than 100° C.,preferably 80° C. to 95° C., in an atmosphere reduced to a pressure atwhich the boiling point of water is less than 100° C., preferably 80° C.to 95° C., and the material then is blown with air and, thereafter, thematerial is dried by vacuum drying, shaking off, gas blowing, heating.

According to the fourth embodiment (4) of the present invention,depending on the material to be washed and/or the causative substance ofcontamination, it is not necessary to dip the material into an aqueoussolution of a surfactant having a water repellency. Thus, after washingin a conventional manner, not via the step of attaching the alignedmolecular layer of the water repellent surfactant, the material to bewashed may be placed in a vacuum kettle, then heated with steam at atemperature of less than 100° C., preferably 80° C. to 95° C., in anatmosphere reduced to a pressure at which the boiling point of water isless than 100° C., preferably 80° C. to 95° C. Subsequently, afterblowing the material with gas such as air, the material is dried byvacuum drying. Thus, the desired washing/drying can be performed. Thismethod can be applied to the case when washing with an aqueous solutionother than an aqueous solution containing a surfactant having a waterrepellency therein.

According to the fifth embodiment of the present invention, awashing/drying apparatus for carrying out washing/drying by use of anaqueous solution of a water repellent surfactant, as shown in FIG. 2,has a water tank 6 for containing an aqueous solution of a surfactanthaving a water repellency, a shower washing device for removingsuperfluous surfactant attached to the material W to be washed in thewater tank 6, and a vacuum chamber 12 for drying the material to bewashed after shower washing.

The vacuum chamber 12 has a means of jetting steam so that the materialW to be washed can be heated with steam at a temperature less than 100°C., preferably 99° C. or lower and more preferably 80° C. to 95° C., inan atmosphere reduced to a pressure at which the boiling point of wateris less than 100° C., preferably 99° C. or lower and more preferably 80°C. to 95° C., and further, has gas blowing means so that the water canbe subsequently drained by blowing gas such as air. The means of jettingsteam and the gas blowing (e.g., air blowing) means may commonly use ablowing means (nozzle).

As the above-mentioned water repellent surfactants, the surfactants suchas hydrocarbon type surfactents having an alkyl chain length of thehydrophobic group of 12 to 18 in the hydrocarbon type, fluorine typesurfactants having an alkyl chain length of the hydrophobic group of 6to 12 in the fluorine type and a water-repellent silicone typesurfactants may be employed.

There are no specific limitations to the conditions for dipping thematerial to be washed in an aqueous washing solution containing awater-repellent surfactant, and any conditions capable of forming atleast one molecular layer of the water repellent surfactant on thesurface of the material to be washed can be adopted, as long as at leastone molecular layer of the water repellent surfactant is attached to thesurface of the material. Although the preferable conditions may bevaried depending upon the kinds of surfactants used, the preferableconcentration of the surfactant in the aqueous, washing solution is 300ppm or more, particularly 450 to 5000 ppm, the preferable temperature is30° C. to less than 100° C., particularly 40° C. to 60° C., and thepreferable dipping time is 10 sec or more, particularly 30 sec to 2 min.

According to another aspect of the present invention, there is provideda drying apparatus for drying, after thorough washing of materials (orarticles) such as non-metallic (e.g., plastic) precision parts,electronic parts, non-metallic (e.g., plastic) cases for accommodatingparts, by removing water or moisture adhered thereto by irradiatingelectromagnetic waves to the material to be dried thereby to heat themoisture adhered thereto, and, during or after heating the moisture, gasblowing, vacuum drying or centrifugal drying.

As mentioned above, according to the present invention, the waterrepellent surfactants and the other surfactants are added to an aqueouswashing solution to enhance the detergency thereof, but this causes aproblem of foaming during the above-mentioned circulating and filteringprocess, which comprises passing the washing solution through a finefilter and which is performed for maintaining a desired cleanlinessfactor of the washing solution. FIG. 8 shows the usual washing system,i.e., a system for circulating a washing solution obtained by adding asurfactant to water.

In this system, the washing solution 26 is pumped from a heat-exchangevessel 27 into a filter 28 and finely filtered, and then is transferredto a washing vessel 29. While the washing solution is being pumped, thesolution in the washing vessel 29 overflows through the upper portionthereof into an overflow vessel 30 disposed at the brim of the vessel29, and contaminants such as oil adhered to the materials to be washedare removed, because the contaminants float on the surface of thewashing solution in the washing vessel 29, since they have a specificgravity lower than that of the washing solution. The overflow of thewashing solution 26 is performed to prevent a readhering of thecontaminants to the material which has been washed, when removed fromthe vessel. The washing solution 26 overflows into the overflow vessel30 and is returned to the heat-exchange vessel 27 through a drainagepiping 31, and thus the washing solution 26 is continuously recycled andfiltered to maintain a desired cleanliness thereof. In general, thewashing solution 26 is heated to enhance the washing ability, but inthis case, a part of the water is evaporated, and correspondingly, thelevel of the washing solution is lowered and the concentration of thesurfactant cannot be maintained at a desired constant level. Therefore,it is necessary to add water to the solution in an amount correspondingto that lost through evaporation. This is effectively performed byautomatically supplying water through an inlet 34 past an automaticvalve 35 by the action of a level sensor 32 affixed to the heat-exchangevessel 27, and wherein 36' denotes a heater.

Air is mixed in the washing solution 26 when the solution in theoverflow vessel 30 enters the drainage piping 31, and as a result, foam33 is generated on the surface of the solution retained in theheat-exchange vessel 27. The foam 33 is continuously generated, and in ashort time, overflows from the heat-exchange vessel 27. In addition, theforegoing level sensor 32 is lifted by the action of the generated foam,and thus does not act as required.

According to a further aspect of the present invention, however, theabove-mentioned generation of foam observed when a washing solutionwhich is liable to cause foaming is subjected to the above-mentionedcirculation, can be effectively suppressed or prevented.

In general, the amount of washing solution 26 discharged through thedrainage piping 31 is greater than that pumped into the washing vesselby the action of the circulation pump p shown in FIG. 8, andaccordingly, air is mixed in the washing solution 26, and therefore,foam is generated. Conversely, if the amount of washing solution 26discharged through the drainage piping 31 is smaller than that pumpedinto the washing vessel by the action of the circulation pump, the waterlevel in the overflow vessel 30 rises, and within a short time, thewashing solution 26 overflows from the overflow vessel 30.

According to the foam-suppressing apparatus of the present invention,the foaming can be effectively prevented because the overflow vessel 30is filled with the washing solution 26, to a level at which the air isnot mixed in the solution 26, and the flow rate of the washing solution26 discharged through the drainage piping 31 is automatically controlledso that the amount thereof is equal to that pumped into the washingvessel 29 by the circulating pump.

In the first embodiment according to the first aspect of the presentinvention, by dipping a material to be washed into an aqueous solutioncontaining a surfactant having a water repellency (which repels water)before drying by a known drying method such as vacuum drying, shakingoff, gas blowing (e.g., air blowing), and heating, at least onemolecular layer of a water repellent surfactant is attached to thesurface of the material to be washed. This also functions to wash thematerial to be washed, and if the product has been already washed inanother step, the object is to attach at least one molecular layer ofthe water repellent surfactant to the surface of the material to bewashed, as a pre-treatment to the washing step.

The aqueous solution containing a surfactant having a water repellencyis not an excellent washing solution in itself, but will exhibit astrong washing ability when used, for example, in combination with asonication washing. Depending on the material to be washed and/or thecausative substance of contamination, a sufficient washing can becarried out by using an aqueous solution of a surfactant having a waterrepellency as the washing solution.

Thus, when an aqueous solution containing a surfactant having a waterrepellency as the washing solution, after washing with an aqueoussolution containing a surfactant having water repellency, when drawingup the material to be washed from the water tank, the surfactant will beattached in a state in which at least one molecular layer is alignedthereon. As a result, the surface of the material to be washed has agood water repellency, whereby the water becomes beaded, and bythereafter carrying out drying by a known drying method such as vacuumdrying, shaking off, gas blowing (e.g., air blowing), and heating, itcan be easily and rapidly dried.

Namely, when the material is washed with an aqueous solution containinga surfactant having a water repellency, since the washing solutionitself has a water repellency, it has a good dryability, and drying canbe easily and rapidly effected by subsequently drying in a conventionalmanner such as shaking off, gas blowing (e.g., air blowing), andheating.

In contrast, when the material is washed with an aqueous solution otherthan the aqueous solution containing surfactant having a waterrepellency, the subsequent drying becomes difficult. Nevertheless, evenafter washing with such an aqueous solution having no water repellency,preferably the material to be washed is dipped in an aqueous solutioncontaining a surfactant having a water repellency as a pre-treatment,before drying and after washing. After dipping, when draining thematerial to be washed, at least one molecular layer is attached to thesurface of the material to be washed, as described above, whereby awater repellency is created on the surface of the material to be washed,and thereafter, drying can be rapidly carried out by a conventionaldrying method such as vacuum drying, shaking off, gas blowing (e.g., airblowing), and heating.

In the second embodiment according to the first aspect of the presentinvention, as described above, when dipped into an aqueous solutioncontaining a surfactant having a water repellency, said surfactant isattached as at least one molecular layer to the surface of the materialto be washed, whereby the water on the surface of the material to bewashed becomes beaded and can be easily removed when dried. For amaterial which is particularly difficult to dry, such as a part having acomplicated shape, even if the surface has a water repellency, thedrying is insufficient when using only known drying methods such asvacuum drying, shaking off, gas blowing (e.g., air blowing), andheating.

By heating, after blowing steam against the material to be washed, theviscosity of the water will be lowered and it will be readilyevaporated, whereby the drying becomes easier. Since, however, water hasa high boiling point of 100° C., just blowing steam against thematerial, depending on the material to be washed, overheats thematerial, and thus the material to be washed may be damaged. Further,the attached molecular layer of the surfactant will be removed.

Accordingly, the present invention employs a method in which the heatingis effected with steam but in an atmosphere reduced to a pressure suchthat the temperature does not reach 100° C. In a reduced pressureatmosphere, the boiling point of water will be lowered and becomes lowerthan 100° C., which is the boiling point under atmospheric pressure.Therefore, depending on the properties of the material to be washed, andso that the boiling temperature is such that the attached molecularlayer of the surfactant is not removed, the pressure of the atmospherein the steam heating treating portion is reduced.

Thus, by effecting steam heating at a relatively lower temperature, sothat the material to be washed is not damaged and the attached molecularlayer of the surfactant is not removed, the viscosity of the water onthe surface of the material to be washed is lowered and a latentevaporation heat is given thereto, whereby the subsequent drying can beeffected by only a conventional drying means such as vacuum drying,shaking off, gas blowing (e.g., air blowing), heating.

In the third embodiment according to the first aspect of the presentinvention, as described above, by steam heating the material to bewashed at a relatively lower temperature to an extent such that it isnot damaged and the aligned molecular layer of the surfactant is notremoved, it can be dried by a conventional drying means such as vacuumdrying, shaking off, gas blowing and (e.g., air blowing), heating withrelative ease, but will take a long time to dry, and a very complicatedmaterial becomes difficult to dry.

If after the steam heating at a low temperature as described above,blowing with air is carried out, the water shaped in beads on thesurface of the material to be washed is blown off. If hot air is used atthis time, then the material to be washed (which has been previouslyheated by steam) cannot be cooled, and therefore, the latent heatnecessary for evaporation of the water is supplied, and drying will alsoproceed by evaporation.

Even after blowing with air, water remains at sites where the blown aircannot reach, such as a sink, etc., but since a vacuum drying issubsequently effected according to the present invention, water in thesinks, etc., will be removed by suction, whereby a rapid drying can beachieved with a material to be washed that has a complicated shape andis difficult to dry.

In the fourth embodiment according to the first aspect of the presentinvention, as described above, after the aqueous solution containing asurfactant having a water repellency has been added and drawn up, mostpreferably a steam heating under a reduced pressure, a blowing with, forexample, air, or a vacuum drying is carried out. Nevertheless, dependingon the kind of material to be washed, without a dipping thereof into theaqueous solution containing a surfactant having a water repellency, asufficient drying is possible only by using a combination of heatingwith a low temperature steam of less than 100° C., preferably 99° C. orlower, more preferably 80° C. to 95° C., and blowing with, for example,air, and then vacuum drying.

More specifically, after washing with an aqueous solution other than theaqueous solution containing a surfactant having a water repellency, whenthe material to be washed is placed in a vacuum kettle to be brought toa reduced pressure, and heated with low temperature steam at 99° C. orlower, the viscosity of water is lowered and becomes more readilyvaporizable by heat. Accordingly, when blowing with air is subsequentlyconducted, the water is easily blown off. Then, due to the subsequentvacuum drying, water in the sinks, etc., is easily removed by suction.

A series of these treatments can be carried out in a single vacuumchamber, and are easily workable. Namely, the vacuum kettle containingthe material to be washed may have a reduced pressure and be heated withsteam, then the feeding of steam is discontinued and the nozzle isswitched to an air source, whereby air is blown therein. Subsequently,the air blowing is stopped, and a vacuum drying is performed to completethe series of drying treatments.

In the fifth embodiment according to the first aspect of the presentinvention, as the surfactant having a water repellency there are knownthe hydrocarbon type, the silicon type and the fluorine type, but thehydrocarbon type and the fluorine type are most suited for this washingand drying. In the case of the hydrocarbon type, surfactants with ahydrophobic group having an alkyl chain length of 12 to 18, and in thefluorine type those with an alkyl chain length of 6 to 12, arepreferable.

The washing/drying apparatus of the present invention, i.e., theapparatus which performs the washing and drying by using an aqueoussolution of a water repellent surfactant, is provided with washingdevices next to the washing vessel holding an aqueous solution of asurfactant having a water repellency, and therefore, superfluoussurfactant on the material to be washed is removed by a shower washing,and thus a necessary minimum amount of the water repellent surfactant isalways attached to the surface of the material to be washed, whereby thewater repellent effect can be stably maintained.

The apparatus also is provided with a vacuum chamber for drying thematerial to be washed after the shower washing. The vacuum chamber has ameans for jetting steam such that the material to be washed can beheated by steam at a temperature of less and than 100° C., preferably99° C. or less and more preferably 80° C. to 95° C., in an atmospherehaving a reduced pressure, so that the boiling point is less than 100°C., preferably 99° C. or less, more preferably 80° C. to 95° C., andfurther, has a blowing means whereby water can be removed by blowing gas(e.g., air).

To accomplish this, the three treatments, i.e., low temperature steamheating, gas blowing and vacuum drying, are conducted continuously by asingle vacuum chamber, to give a better workability and simplify theapparatus.

According to the first embodiment of the second aspect of the presentinvention, the moisture adhered to the surface of the non-metallicprecision parts, electronic parts and cases for accommodating the partsis heated by irradiating these materials with electromagnetic waves of2450 MHz, without heating the subject per se. The higher the irradiationpower of electromagnetic waves and the longer the irradiation time, thehigher the heating rate of the moisture adhered to the surface of thesematerials. The temperature of the heated moisture is at highest 100° C.In addition, the coefficient of thermal conductivity of the materials tobe washed, such as those of plastics per se, is very small. Therefore,if the material is irradiated with the electromagnetic waves whileblowing, for example, air, thereon, the water drops always move over thesurface of the material to be washed and the temperature of the materialper se does not rise. Thus, the irradiation with the electromagneticwaves does not exert any detrimental influence on the material, such asthermal deformation. When a material which is liable to suffer thermaldeformation is treated, the foregoing detrimental effects such asthermal deformation can be effectively eliminated by lowering theirradiation power of the electromagnetic waves, by intermittentlyirradiating the material with the electromagnetic waves, or bycontrolling the irradiation power or the length of the irradiation timewhile detecting the temperature of the material to be washed, using aninfrared radiation thermometer.

As explained above, if the material to be washed is subjected to airblowing while heating the moisture adhered to the material through theirradiation with the electromagnetic waves, the material can beeffectively dried without an adverse affect, such as heat deformation,on the material.

In addition, it is also possible to perform the gas-blowing, such as theair-blowing, after the material is heated through the irradiation withthe electromagnetic waves, without an adverse affect on the material,depending on the kind of the material to be washed. For example, this istrue in cases wherein the heat resistance of the material to be washedis very high or the material has a shape which can prevent the residenceof water therein or thereon, and thus is not damaged by the residencethereon of water at a high temperature.

According to the second embodiment of the second aspect of the presentinvention, the moisture adhered to the surface of the non-metallicprecision parts, electronic parts and cases for accommodating the partsis heated by irradiating these materials with electromagnetic wave of2450 MHz without heating the materials per se. The higher theirradiation power of electromagnetic waves and the longer theirradiation time, the higher the heating rate of the moisture adhered tothe surface of these materials. The temperature of the heated moistureis at highest 100° C. under the atmospheric pressure, but if thematerial is heated through the irradiation with the electromagneticwaves under a reduced pressure in the vacuum chamber, the boiling pointof water can be arbitrarily reduced by controlling the degree of vacuum.Thus, if the material is heated through the irradiation with theelectromagnetic waves at a reduced pressure of not more than thepredetermined level corresponding to the degree of vacuum which ensuresthat the temperature of the material is not higher than theheat-resisting temperature thereof throughout the irradiation with theelectromagnetic waves, the temperature of the material per se does notrise, and thus the irradiation with the electromagnetic waves does nothave an adverse affect on the materials, such as thermal deformation.

As explained above, if the material to be washed is heated to remove themoisture adhered to the material through the irradiation with theelectromagnetic waves under a reduced pressure in the vacuum chamber,the material can be effectively dried without an adverse affect, such asheat deformation, on the material.

In addition, it is also possible to perform the treatment under areduced pressure after the material is heated through the irradiationwith the electromagnetic waves, without an adverse affect on thematerial, depending on the kind of the material to be washed. Forexample, this is true in cases wherein the heat resistance of thematerial to be washed is very high or the material has a shape which canprevent the residence thereon of water, and thus is not damaged by theresidence thereon of water at a high temperature.

According to the third embodiment of the second aspect of the presentinvention, the moisture adhered to the surface of the non-metallicprecision parts, electronic parts and cases for accommodating the partsis heated by irradiating these materials with electromagnetic wave of2450 MHz, without heating the materials per se. The higher theirradiation power of electromagnetic waves and the longer theirradiation time, the higher the heating rate of the moisture adhered tothe surface of these materials. The temperature of the heated moistureis at highest 100° C.

In addition, the coefficient of thermal conductivity of the materials tobe washed, such as those of plastics per se, is very small. Therefore,if the material is irradiated with the electromagnetic wave while thematerial is subjected to centrifugation, the water drops always moveover the surface of the material to be washed and the temperature of thematerial per se does not rise, and thus the irradiation with theelectromagnetic waves does not have an adverse affect on the materials,such as thermal deformation. When a material which is liable to sufferthermal deformation is treated, the foregoing detrimental effects suchas thermal deformation can be effectively eliminated by lowering theirradiation power of the electromagnetic waves, by intermittentlyirradiating the material with the electromagnetic waves, or bycontrolling the irradiation power or the length of the irradiation timewhile detecting the temperature of the material to be washed, using aninfrared radiation thermometer.

As explained above, if the material to be washed is heated to remove themoisture adhered to the material through the irradiation with theelectromagnetic waves while the material is subjected to centrifugation,the material can be effectively dried without an adverse affect, such asheat deformation, on the material.

In addition, it is also possible to perform the treatment bycentrifugation after the material is heated through the irradiation withthe electromagnetic waves, without an adverse affect on the material,depending on the kind of the material to be washed. For example, this istrue in cases wherein the heat resistance of the material to be washedis very high or the material has a shape which can prevent the residenceof water, and thus is not damaged by the residence thereon of water at ahigh temperature.

EXAMPLES

Practical embodiments of the washing/drying method, and thewashing/drying apparatus will be described with reference to, but are byno means limited to, the Examples. FIGS. 2 and 3 are examples of theapparatus for performing the washing/drying method of the presentinvention. FIG. 2 shows the steps of the process and a longitudinalsectional view of the apparatus. The apparatus is provided with awashing device or vessel 1 containing an aqueous solution containing asurfactant having a water repellency, a first shower washing device 2, asecond shower washing device 3, a centrifugation drying device 4, and avacuum drying device 5, arranged in this order.

In FIG. 2, the washing device 1 contains an aqueous solution 7,containing a surfactant having a water repellency, received in a watervessel 6, and having a sonication generation device 8 provided therein.The washing device 1 is adapted to recover the flow of contaminantsgenerated by washing, heat same in the heating water vessel 9, and toclean same with the filter 10 for reuse.

The first shower washing device 2 and the second shower washing device 3jet pure water against the material W to be washed, to wash off theprevious washing liquid.

The centrifugal drying device 4 removes water by centrifugal force, byrotating the basket 11, in which the material W to be washed is placed,by the motor M.

The vacuum drying device 5 removes water by suction, by reducing thepressure by a vacuum pump VP when the material W to be washed ishermetically sealed in the vacuum chamber 12.

Numeral 13 represents a conveying machine, and to perform the washingand drying when the material W to be washed is placed in the aqueoustank 6 containing the aqueous solution 7 of a surfactant having a waterrepellency is added, the sonication generating device 8 is driven toremove contamination and dust on the surface of the material W to bewashed. After completion of the washing, the material W to be washed issuspended from the conveying machine 13 and conveyed thereby to thefirst shower washing device 2, and the surfactant having a waterrepellency will be attached thereto, while aligned in at least onemolecular layer on the surface of the material W to be washed, after thewashing.

In practice, rarely is only one molecular layer attached, and usually aplural number of molecular layers are present. Therefore, in the firstshower washing device 2, the aqueous solution of the surfactant having awater repellency is washed off with pure water. If the superfluous waterrepellent surfactant can be removed only with the pure water jetting bythe first shower washing device 2, this pure water shower washing alonewill suffice as the first step, but if not, then the material W isconveyed to the second shower washing device 3 to be again washed withpure water. Accordingly, at least one molecular layer of the surfactanthaving a water repellency is attached to the surface of the material Wto be washed.

After having thus removed superfluous water repellent surfactant, dryingis carried out in a conventional manner. That is, in the centrifugationdrying device 4, the material W to be washed is placed in a basket 11,which is rotated by a motor M, and the water is removed by centrifugalforce. Alternatively, when the material W is hermetically sealed in thevacuum chamber 12, the pressure is reduced by a vacuum pump VP toaspirate the water by suction.

Although superfluous surfactant can be removed by only shower washing,as described above, at least one molecular layer remains on the surfaceof the material W, whereby the requisite water repellency can bemaintained to repel water, and the water attached thereto is beaded. Asa result, the water will fall off under its own weight, and therefore,compared with the case of using a surfactant having no water repellency,or when not using a surfactant, the amount of water attached will bereduced to about 1/3, and thus the load at the next drying step will bealleviated.

Further, the surface of the film on which the water repellent surfactantis attached repels water, as mentioned above, to form water beads, andthese beads can be easily removed even by a conventional drying methodsuch as centrifugal force or a vacuum aspiration.

For drying after the pure water shower washing, in addition to thecentrifugal separation or vacuum drying processes, there also may beemployed methods such as blowing for example, air, onto the material Wor heating same.

The vacuum chamber 12 of the vacuum drying apparatus 5 has a means forjetting steam, whereby the material W to be washed can be heated withsteam at a temperature of less than 100° C. in an atmosphere having areduced pressure at which the boiling point of the water is less than100° C., and further, has a blowing means whereby the water can beremoved by blowing gas such as air thereon.

Therefore, by jetting steam under a reduced pressure, the material to bewashed can be heated with steam at a temperature of less than 100° C.,preferably 80° C. to 95° C., as mentioned above. This steam heatinglowers the surface tension of the water, and further, heats the materialW to be washed to thereby make the water readily vaporizable. In thesame vacuum chamber 12, the water is then blown off by blowing a normaltemperature gas (e.g., air) or hot gas (e.g., air) thereon, and then thewater discharged by suction under a vacuum.

After steam heating is effected when the boiling point is thus lowered,a vacuum chamber 12 capable of gas (e.g., air) blowing is provided, andas mentioned above, this is also effective for drying, after a waterwashing not using an aqueous solution of a water repellent surfactant.

The temperature of the low temperature steam depends on the pressure,and therefore, the limit is about 40° C. at about -700 mHg, which is thecapacity of a conventional vacuum pump; further lowering of thetemperature can be made by improving the capacity of the vacuum pump.

The apparatus in FIG. 2 is intended to enhance the drying effect byperforming washing with an aqueous solution of a water repellentsurfactant, and utilizing the water repellent effect of the waterrepellent surfactant attached to the surface of the material W to bewashed after washing, but in the case of a material (or article) towhich oil is adhered, such as a material W to be washed after mechanicalworking, a proper wash can be obtained only by using the water repellentsurfactant and the sonication generation apparatus in combination.

Thus, in the case of a material W to be washed to which an oilycomponent is adhered, after previously washing the material with an oilycomponent in a special washing vessel 14 as shown in FIG. 3, thematerial w is washed in a shower washing device 15. Then, using aconveying machine 13, the material W is transferred to a washing device1 containing the aqueous solution of the water repellent surfactantshown in FIG. 2, and the water repellent surfactant is attached thereto.In this case, the sonication generation device 8 in the water vessel 6should not be driven, but when the material W to be washed after oilcomponent is removed is to be rewashed with the aqueous solution of thewater repellent surfactant, the sonication generation device 8 is drivento perform the washing. The subsequent procedures are as described inFIG. 2.

In FIG. 3, the oily component washing vessel 14 has an aqueous solution16 containing an alkaline defatting agent (e.g., Fine Cleaner FC35available from Nippon Perkarizing Co.) suitable for oil washing in thewater vessel, and has the sonication generation device 8 therein. Theoily component floating on the surface is recovered by the recoverydevice 17, and then the liquid surface portion alone is recovered by theoil collecting float 18, and thereafter, the oily component is separatedand removed in the oil separating device 19.

Next, the surfactant having a water repellency, and the washing anddrying conditions, are described. In the present invention, washing withan aqueous solution containing a surfactant having a water repellency,or a drying pre-treatment after washing is practiced. Therefore, asurfactant having a strong washing effect and a water repellency isrequired. More specifically, it is important to use a surfactant tolower the surface tension and increase the wettability andpenetrability. Generally, as the surfactant, there are known thehydrocarbon type, silicon type and fluorine type, but as a result of astudy by the present inventors, the fluorine type surfactants having thefollowing characteristics are most preferable for attaining the objectsof the present invention:

(1) A very high ability to lower the surface tension. For example, forthe fluorine type: 1.5 dyn/cm, the silicone type: 22 dyn/cm, and thehydrocarbon type: 30 dyn/cm.

(2) A good water repellency and oil repellency.

(3) An excellent heat-resistant stability.

(4) Little (i.e., is reduced) toxicity.

Thus, when a surfactant having a water repellency and having a lowsurface tension is used, the washability is enhanced and the amount ofwater attached becomes smaller (i.e., is reduced), whereby anenhancement of the dryability can be expected. Also, due to the oilrepellency, the oil liberated from the material to be washed can be moreeasily recovered by the oil separation device, and reattachment of theoil component to the material to be washed can be prevented.

For the fluorine type surfactants, the optimum treatment conditions forlowering the amount of water attached were investigated. In theExperiments, the anionic type, i.e., perfluoroalkyl carboxylate (S-113)and perfluoroalkyl phosphate (S-112), the nonionic type, i.e.,perfluoroalkylamine oxide (S-141) and the cationic type, i.e.,perfluoroalkyl trimethylammonium salt (S-121), were tested by varyingthe temperature and the treatment time. The sample materials to bewashed were an aluminum plate (i.e., aluminum A 5052) having a size of50 mm×50 mm×1 mm.

Experiments were conducted by varying the temperature by 10° C. in arange of 30° C. to 70° C., and the dipping time was made 15, 30, 45, 60,90, and 120 seconds. The results are shown in Table 1.

                  TABLE 1                                                         ______________________________________                                                        Dipping time (sec)                                            Temp.           (Degree of water wetting)                                     (C.°)                                                                         Surfactant                                                                             15      30   45    60   90    120                             ______________________________________                                        30     S-113    95%     90%  85%   85%  80%   80%                                    S-112    100%    100% 100%  100% 100%  95%                                    S-141    100%    100% 100%  100% 95%   90%                                    S-121    100%    100% 100%  100% 90%   90%                             40     S-113    95%     85%  80%   70%  50%   5%                                     S-112    100%    100% 100%  95%  95%   90%                                    S-141    100%    100% 100%  90%  90%   85%                                    S-121    100%    100% 100%  100% 90%   90%                             50     S-113    90%     80%  50%   5%   0%    0%                                     S-112    100%    100% 100%  95%  90%   80%                                    S-141    100%    100% 95%   95%  90%   80%                                    S-121    100%    100% 100%  100% 90%   80%                             60     S-113    80%     70%  5%    0%   0%    0%                                     S-112    100%    100% 95%   90%  80%   60%                                    S-141    100%    100% 90%   90%  80%   70%                                    S-121    100%    100% 100%  100% 90%   80%                             70     S-113    70%     5%   0%    0%   0%    0%                                     S-112    80%     75%  65%   50%  20%   0%                                     S-141    80%     80%  60%   50%  30%   10%                                    S-121    100%    100% 100%  100% 80%   70%                             ______________________________________                                    

As a result, it was found overall that a higher temperature and a longerdipping time reduces the amount of water attached. Among the anionic,nonionic and cationic types, the amount of water attached was thesmallest with the anionic type, followed by the nonionic type. Among theanionic type, a perfluoroalkyl carboxylate leaves a particularly smallamount of water attached, and a perfluoroalkyl phosphate issubstantially the same as a perfluoroalkylamine oxide.

As a result, a perfluoroalkyl carboxylate of the anionic type was foundto provide the highest water repellency. In the case of a perfluoroalkylcarboxylate of the anionic type, the amount of water attached was zerowhen dipped at 50° C. for 90 seconds or longer, at 60° C. for 60 secondsor longer, and at 70° C. for 45 seconds or longer.

A perfluoroalkyl carboxylate has a chain structure as shown in FIG. 4,and although the alkylcarbon chain length in this Figure is 8, analkylcarbon length of about 6 to 12 in the water repellent surfactant ofthe fluorine type provided an excellent water repellency. In thisconnection, the hydrocarbon type with alkylcarbon chain lengths of about12 to 18 also had an excellent water repellency.

Next, for the surfactant water repellency, the concentrations when usingperfluoroalkyl carboxylates were determined at 40° C., 50° C., and 60°C., when the perfluoroalkyl carboxylate concentration was varied to 30ppm, 150 ppm, 300 ppm, 1500 ppm, and 3000 ppm, and the dipping timefixed at 1 minute. The results are shown in Table 2.

                  TABLE 2                                                         ______________________________________                                        Temp.  Conc. of Perfluoroalkylcarboxylate                                     (°C.)                                                                         30 ppm   150 ppm   300 ppm                                                                              1500 ppm                                                                             3000 ppm                              ______________________________________                                        40     100%     100%      50%    30%    30%                                   50     100%     100%      20%    0%     0%                                    60     100%     90%       0%     0%     0%                                    ______________________________________                                    

As shown in Table 2, even when the concentration was 3000 ppm at 40° C.,the amount attached was about 30%. At 50° C., when the concentrationbecame 1500 ppm or higher, the amount of water attached was zero, and at60° C., at a concentration of 300 ppm or more, the amount of water waszero. Therefore, at a dipping time of 1 minute and a liquid temperatureof 60° C., the amount of water attached can be made zero if theconcentration is made 300 ppm or higher.

Next, detailed examinations at about around 300 ppm while varying thedipping time to 30 seconds, 1 minute, and 1 minute and 30 seconds werecarried out. The results are shown in Table 3.

                  TABLE 3                                                         ______________________________________                                                   Conc. of Perfluoroalkylcarboxylate                                 Temp.  Dipping   240     300   450   600   900                                (°C.)                                                                         time      ppm     ppm   ppm   ppm   ppm                                ______________________________________                                        40     30 sec    100%    100%  95%   95%   95%                                       1 min 00 sec                                                                            100%    50%   40%   40%   40%                                       1 min 30 sec                                                                            100%    40%   30%   20%   10%                                50     30 sec    100%    90%   90%   85%   50%                                       1 min 00 sec                                                                            90%     20%   20%   5%    5%                                        1 min 30 sec                                                                            80%     10%   0%    0%    0%                                 60     30 sec    100%    80%   60%   20%   20%                                       1 min 00 sec                                                                            80%     10%   0%    0%    0%                                        1 min 30 sec                                                                            70%     0%    0%    0%    0%                                 ______________________________________                                    

As is clear from the results shown in Table 3, by dipping at 50° C. for1 minute and 30 seconds and making the concentration 450 ppm or more,the amount of water attached was zero. At 60° C., at concentrations of450 ppm or more, by dipping for one minute, the amount of water attachedwas zero, and by dipping for 1 minute and 30 seconds, at concentrationsof 300 ppm, the amount of water attached was zero. Therefore, by dippingat 60° C. for one minute, to obtain a high water repellency, theconcentration must be made 450 ppm or higher.

Further, since the surface tension of pure water with a perfluoroalkylcarboxylate can be lowered to about 17 dyn/cm by an addition of 300 ppmthereof, from the standpoint of the surface tension, a concentration of300 ppm or more is desirable, but in view of the treatment margin, about600 ppm is most preferable. The surface tension is 73 dyn for pure waterand 20 dyn for Freon 113.

Next, in an aqueous solution with a perfluoroalkyl carboxylateconcentration of 600 ppm, which is the optimum concentration, bydetermining the amount of water attached after sonication washing (i.e.,frequency 28 kHz, power 200 W) at a liquid temperature of 60° C. for 1minute, the water repellent effect was evaluated. As a result, amaterial subjected to sonication washing in an aqueous solution withammonium perfluoroalkyl carboxylate (concentration: 600 ppm) had about1/3 the amount of water attached compared with material washed only withpure water. Further, when subjected to air blowing (air at 6 kg/cm² Gwas blown for 3 sec. at a distance of 50 cm), compared with a materialsubjected to air blowing after washing only with pure water, the amountof water attached became 1/1000 or lower. Thus, by removing water by airblowing after washing with an aqueous solution of a water repellentsurfactant, the drying effects are enhanced.

Nevertheless, even if the amount of water attached is greatly reduced, acomplete drying cannot be effected, and therefore, a heating of thematerial to be washed was investigated as a method of realizing acomplete drying. This is because heating the material to be washedresults in a lowering of the viscosity of water, and promotes an easiervaporizability by heat. Particularly, in contrast to the vaporizationheat of Freon 113, which is 35 cal/g, that of water is greater by15-fold at 539 cal/g, having a greater heat content necessary for watervaporization, and therefore, it is important to previously provide alarge amount of heat to the material to be washed.

Accordingly, as a result of an investigation of heat sources, comparedwith hot water or hot air, steam heating was found to be most effective.Steam has a large amount of heat storage, and can be heated at a highspeed, and therefore, a sufficient heat content for vaporizing water canbe provided.

Nevertheless, since the boiling point of water is as high as 100° C.,depending on the kind of the material to be washed, there is a fear thatthe material to be washed may be damaged, and that the aligned molecularlayer of the surfactant intentionally attached thereto will be removed.

Accordingly, in the present invention, although heating is done withsteam, a method of blowing steam in a reduced atmosphere wherein thetemperature will not become as high as 100° C. was attempted. As aresult, when steam was jetted by reducing the pressure so that theboiling point of water was less than 100° C., preferably 99° C. orlower, more preferably 80°-95° C., it was found that water iseffectively removed but the aligned molecular layer of the surfactant isnot removed. Therefore, depending on the properties of the material tobe washed, preferably the temperature of the jetting steam is withinthis range.

It has been found that a low temperature steam heating is indispensable,but the following various experiments and improvements as shown belowwere repeated, to further enhance the drying effect:

(1) Vacuum drying alone conducted after low temperature steam heating.

(2) After low temperature steam drying, vacuum drying is effectedfollowed by hot air feeding in a vacuum kettle.

(3) After low temperature steam drying, the lid of the vacuum kettle isopened and hot air is blown therein followed by vacuum drying.

(4) After low temperature steam heating, hot air feeding (dryreplacement) is effected in a vacuum kettle, followed by vacuum drying.

Among the above, the best results were obtained by the method (3) inwhich hot air was blown under an atmospheric pressure after a lowtemperature steam heating, followed by vacuum drying. In the method (1),water remained even after vacuum drying for 30 minutes.

As described above, air blowing was effective, and therefore, airblowing with hot air was attempted, aiming at the effect of air blowingwithout damaging the material or by low temperature steam heating, andextremely good results were obtained. By performing hot air blowing for10 seconds, almost all of the water was blown off and evaporated byheating. When vacuum drying was effected after hot air blowing for 20minutes, the material was completely dried.

In the case of washing a material with a simple shape, vacuum drying isnot always required, but in the case of a material with a complicatedshape, such as one having sinks, etc., a complete drying is renderedpossible only by finally effecting a vacuum aspiration. The vacuumdrying is generally effected at an ambient temperature, but if desired,the vacuum evacuation can be carried out while heating at a temperatureof less than 100° C.

As described above, the best drying method has been determined, anddepending on the kind and properties of the material to be washed andthe substance causing the contamination, it is clear the material can bewashed even with an aqueous solution of a water repellent surfactant fora drying pre-treatment, without the need for a special washing as shownin FIG. 3.

For example, an aluminum sample treated with Arosin was coated withthree kinds of cutting oils, (i.e., GM5, GS5, and FW68, all availablefrom Nippon Oil Co., Ltd) and was subjected to sonication washing (i.e.,28 kHz×200 W)in the above-mentioned aqueous perfluoroalkyl carboxylatesolution at 60° C. for 1 minute, then shower washed with pure water anddried. As a result, for all three oils, no oil staining was found, andthus a good defatting treatment was effected.

Regarding the effect when washing away dust, washing with an aqueoussolution of water repellent surfactant according to the presentinvention was found to give a better effect than washing with aconventional fluorocarbon as in the prior art, with a residual useamount of about 1/10 or less.

Next, the effect on the material to be washed, when washed and driedaccording to the method of the present invention, was investigated. Thematerials to be washed were two kinds of Kanizen plated products, twokinds of Arosin plated products, and one kind of battery oxidizedtreated product, and the corrosion resistance thereof was tested. As aresult, no abnormality was found in any of the five products. Also,after Cellophane tape was adhered thereto, an adhesion test wasconducted by peeling the tape from the material, but no abnormality wasfound in any of the five products.

According to an aspect of the present invention, there is provided anapparatus for water-draining and drying non-metallic precision parts,electronic parts and cases for accommodating parts which have beenthoroughly washed with water by blowing air or the like thereon, duringor after irradiating these materials with electromagnetic waves to heatthe moisture adhered thereto. As shown in the top plan and saidelevational schematic views of FIGS. 5A and 5B, respectively, theapparatus comprises a rotatable table 21 which makes it possible toefficiently heat the material W to be washed and an electromagneticwave-irradiation device 22 capable of irradiating the material withelectromagnetic waves of 2450 MHz, thereby heating the moisture adheredto the material, and an air-blower device 23 for blowing, for example,air onto the material to remove the heated moisture on the material, tothus water-drain or dry the same. The table 21 need not be rotatable, asthis depends on the shape of the material W. Note, 25 denotes a lid.This rotating system can be also applied to the shower washingapparatus, whereby the water blow nozzles can be placed so that thewater shower comes from only one or two directions.

An apparatus shown in the top plan and side elevational schematic viewsof FIGS. 5A and 5B, respectively, is another drying apparatus forevaporating the moisture adhered to non-metallic precision parts,electronic parts and cases for accommodating the parts which have beenthoroughly washed with water, to dry the materials by applying a reducedpressure to these non-metallic materials w to be washed, during or afterirradiating these materials with electromagnetic waves to heat themoisture adhered thereto. As shown in FIGS. 6A and 6B, the apparatuscomprises a rotatable table 21 which makes it possible to efficientlyheat the material w to be washed, and an electromagneticwave-irradiation device 22 capable of irradiating the material withelectromagnetic waves of 2450 MHz, thereby heating the moisture adheredto the material, and a vacuum pump VP for establishing a reducedpressure or a vacuum to evaporate off and remove the heated moistureadhered to the material, to thus dry the same. The table 21 need not berotatable, as this depends on the shape of the material W.

An apparatus shown in the top plan and side elevational schematic viewsof FIGS. 6A and 6B, respectively, is a further drying apparatus forspin-drying non-metallic precision parts, electronic parts and cases foraccommodating the parts, which have been thoroughly washed with water,by subjecting these non-metallic materials to be washed tocentrifugation, during or after irradiating these materials withelectromagnetic waves to heat the moisture adhered to the materials. Asshown in FIG. 7A and 7B, the apparatus comprises a rotatable table 21which makes it possible to efficiently heat the material W to be washedand an electromagnetic wave-irradiation device 22 capable of irradiatingthe material with electromagnetic waves of 2450 MHz, thereby heating themoisture adhered to the material. The table 21 is also capable of beingrotated at a high speed, and thus the heated moisture on the materialcan be removed by spin-drying.

Next, according to the third aspect of the present invention, thegeneration of foam in the washing solution circulating system can beeffectively suppressed or prevented. Several examples thereof will nowbe illustrated with reference to FIG. 9 to 20.

As shown in FIGS. 9 and 10, according to the present invention, afoam-suppressing means 36 is placed in a washing solution overflowvessel 30 in the circulating system of the washing solution 26 shown inFIG. 8. Various means 36 are shown in FIGS. 11-21.

For example, in the embodiments shown in FIGS. 11 and 12, afoam-suppressing apparatus comprises, in a system for circulating awashing solution, a washing solution overflow vessel 30 capable ofstoring the solution and a valve 39 or 40 which is opened and closed bythe buoyancy force exerted on a float 37 or 38; the valve 39 or 40opening and closing at the water level in the overflow vessel 30 atwhich an exhaust drain 31 for the solution does not entrap air.

In the foam-suppressing apparatus shown in FIGS. 11 and 12, the valve 39or 40 is floated at a level at which the amount of the circulatedsolution entering the overflow vessel 30 is balanced by the flow ratethereof drained through the valve.

A foam-suppressing apparatus shown in FIGS. 13 and 14 comprises, in asystem for circulation a washing solution, an overflow vessel 30 capableof storing the solution, an outer cylinder 41 or 42 connected to anexhaust drain 31 and having a hole through which the solution can enterthe cylinder, and an internal, or inner cylinder 45 or 44 which opensand closes the hole of the outer cylinder 41 or 42 by the buoyancy forceexerted on a float 43 or 44'; the hole of the outer cylinder 41 or 42being opened and closed at the water level in the overflow vessel 30 atwhich the exhaust drain 31 for the solution does not entrap air. Theinternal cylinder 45 or 44 is floated at a level at which the amount ofthe circulated solution entering the overflow vessel 30 is balanced bythe flow rate thereof drained through the hole of the outer cylinder 41or 42.

Note, that the sizes of the holes in the outer cylinder (or sometimes,the inner cylinder) in various embodiments of the present invention canbe any size such that the liquid amount overflowing from the overflowvessel 30 can be satisfactorily withdrawn therefrom.

A foam-suppressing apparatus shown in FIGS. 15 and 16 comprises, in asystem for circulating a solution, an overflow vessel 30 capable ofstoring the solution, an internal cylinder 46 or 47 connected to anexhaust drain 31 and having a hole through which the solution can enterthe cylinder and an outer cylinder 50 or 49 which opens and closes thehole of the internal cylinder 46 or 47 by the buoyancy force exerted ona float 48 or 49'; the hole of the internal cylinder 46 or 47 beingopened and closed at the water level in the overflow vessel 30 at whichthe exhaust drain 31 for the washing solution does not entrap air. Theouter cylinder 50 or 49 is floated at a level at which the amount of thecirculating washing solution entering the overflow vessel 30 is balancedby the flow rate thereof drained through the hole of the internalcylinder 46 or 47.

A foam-suppressing apparatus shown in FIGS. 17 and 18 comprises, in asystem for circulating a washing solution, an overflow vessel 30 capableof storing the washing solution, an internal cylinder 51 or 52 connectedto an exhaust drain 31 and an outer cylinder 55 or 54 having a holethrough which the washing solution can enter the cylinder and in whichthe hole of the outer cylinder is opened and closed by the buoyancyforce exerted on a float 53 or 54'; the hole of the outer cylinder 55 or54 being opened and closed at the water level in the overflow vessel 30at which the exhaust drain 31 for the washing solution does not entrapair. The outer cylinder 55 or 54 is floated at a level at which theamount of the circulated solution entering the overflow vessel 30 isbalanced by the flow rate thereof drained through the hole of the outercylinder 55 or 54.

A foam-suppressing apparatus shown in FIGS. 19 and 20 comprises, in asystem for circulating a solution, an overflow vessel 30 capable ofstoring the washing solution, an outer cylinder 56 or 57 connected to anexhaust drain 31 and an internal cylinder 60 or 59 having a hole throughwhich the solution can enter the cylinder and in which the hole of theinternal cylinder is opened and closed by the buoyancy force exerted ona float 58 or 59; the hole of the internal cylinder 60 or 59 beingopened and closed at the water level in the overflow vessel 30 at whichthe exhaust drain 31 for the solution does not entrap air. The internalcylinder 60 or 59 is floated at a level at which the amount of thecirculating washing solution entering the overflow vessel 30 is balancedby the flow rate thereof drained through the hole of the internalcylinder 60 or 59.

Each of the above-mentioned floats has a cavity therein and a means forexhausting the air from the cavity at the upper portion thereof, so thatthe buoyancy force can be controlled by introducing the washing solutioninto the float.

Furthermore, the shapes of the above-mentioned internal and outercylinders may be, in addition to a circle, any desired cross-sectionalshapes such as a triangle, square and polygonal.

The preferable washing/drying apparatus according to the presentinvention will now be explained with reference to a block diagram/flowchart of FIG. 21, although the present invention is by no means limitedthereto.

In FIG. 21, A is a ultrasonic washing vessel, B a first shower washingvessel, C a dip bubbling vessel, D a second shower washing vessel, andE, E' and E" first, second, and third vacuum drying vessels,respectively.

According to the present invention, the materials/or articles containedin, for example, a basket, are conveyed by an appropriate conveyingmeans from the ultrasonic washing vessel A to the vacuum drying vesselsE, E' and E". The materials to be washed are first dipped in theultrasonic washing vessel A through which an aqueous washing solution ofa fluorine type surfactant is circulated, while the materials to bewashed are subjected to a ultrasonic treatment under the conditions of,1for example, 60° C.×60 sec. Then, the materials to be washed areconveyed to the first shower washing vessel B in which the materials arerinsed by spraying pure water thereon at, for example, 40° C. for 60seconds. At this stage, a layer of substantially one molecule is formedon the surfaces of the materials to be washed. The materials are thendipped in pure water in the dip bubbling vessel C at 40° C. for 60seconds, while clean air is bubbled, whereby the forming of a one molelayer of the surfactant is ensured even in sinks, blind tap holes or thelike, and the materials are further sprayed and washed with pure waterat, for example, 40° C. for 60 seconds.

The materials to be washed having a one molecular layer of a fluorinetype surfactant on the surfaces thereof are, for example, then: (1)heated with a low temperature steam (e.g., 90° C.) under, for example,40 mmHg, (2) subjected to hot air blowing at 90° C. under an atmosphericpressure, and (3) then subjected to vacuum drying under 40 mmHg.According to the present invention, the above-mentioned drying steps(1), (2) and (3) can be effected in series in the vacuum drying vesselsE, E' and E", respectively, as shown by the Solid line in FIG. 21, butaccording to a further preferable embodiment of the present invention,all of the drying steps (1), (2) and (3) are effected in each vacuumvessel of E, E' and E", as shown by corresponding dotted line paths ofFIG. 21. The preferable drying time is 3 to 6 minutes, whereby thedesired through washing and drying can be accomplished.

As described above, according to the present invention, by carrying outa washing treatment by dipping a material to be washed in an aqueoussolution of a water repellent surfactant, or dipping a material to bewashed, which has been first washed in another step, in an aqueoussolution of a water repellent surfactant, at least one molecular layerof the water repellent surfactant is attached to the surface of thematerial to be washed. As a result, due to the water repellent effect ofthe surface of the material to be washed, water is repelled and formedinto beads, whereby a thorough washing and drying after washing can becarried out efficiently without the use of a fluorocarbon and withoutadverse affects on the material to be washed.

Also, by placing the material to be washed in a vacuum chamber, heatingwith steam in an atmosphere having a reduced pressure at which theboiling point of water is controlled to a temperature of 100° C. orless, preferably 99° C. or lower, more preferably 80° C. to 95° C., orair blowing hot air after the steam heating, followed by vacuumaspiration, even an article having a complicated shape, which isdifficult to completely dry, can be fully and rapidly dried.

Further, according to the drying apparatus of the present invention, thematerials, especially those susceptible to heat, can be effectivelydried after washing with water without an adverse affect due to heat.

Furthermore, according to the foam-suppressing apparatus of the presentinvention, the generation of foam in the system can be effectivelysuppressed or prevented by controlling the level of the washing solutionin the overflow vessel for the washing vessel, so that air is notentrapped in the washing solution effluent in the washing solutioncirculating system.

We claim:
 1. A method for washing/drying a material having a surface,comprising the steps of:(a) a first washing step wherein the material iswashed in an aqueous solution containing a surfactant having a waterrepellency; (b) concurrently with step (a), applying sonication to thesolution to remove contamination from the surface of the material; (c)allowing at least one molecular layer of surfactant to form on thesurface of the material during the first washing step; (d) a secondwashing step wherein the material is rinsed with pure water; and (e)drying the material.
 2. The method as recited in claim 1, wherein theconcentration of the surfactant in the aqueous solution is in the rageof 150 ppm to 5000 ppm.
 3. The method as recited in claim 2, wherein aconcentration of the surfactant in the aqueous solution is in the rangeof 450 to 3000 ppm.
 4. The method as recited in claim 2, wherein theaqueous solution has a temperature of less than 100° C.
 5. The method asrecited in claim 1, wherein the surfactant is selected from the groupconsisting of hydrocarbon surfactants having a C₁₂ -C₈ hydrophobic alkylgroup, fluorine surfactants having a C₆ -C₁₂ fluorinated alkyl group,and hydrophobic silicon surfactants.
 6. The method as recited in claim1, wherein the drying step occurs in a reduced pressure atmosphere. 7.The method as recited in claim 1, wherein the drying step occurs using ahot gas blow.
 8. The method as recited in claim 1, further comprisingthe step of:(f) jet-showering the surface of the material with purewater.
 9. The method according to claim 1, wherein the first washingstep occurs for 10 seconds or more.
 10. The method as recited in claim1, wherein the second washing step and the drying step comprise thesubsteps of:rinsing the material in a first shower washing vessel byspraying pure water on the material; dipping the material in pure waterin a dip bubbling vessel while bubbling clean air; spraying and washingthe material with pure water; heating the material with a lowtemperature steam; subjecting the material to hot air; and subjectingthe material to vacuum drying.
 11. The method as recited in claim 1,wherein the drying step is carried out using steam having a temperature≦100° C.
 12. The method as recited in claim 1, wherein the first washingstep occurs from 30 seconds to 2 minutes.
 13. A method forwashing/drying a material having a surface, consisting of the steps:(a)a first washing step wherein the material is washed in an aqueoussolution containing a surfactant having a water repellency; (b)concurrently with step (a), applying sonication to the solution toremove contamination from the surface of the material; (c) allowing atleast one molecular layer of surfactant to form on the surface of thematerial during the first washing step; (d) a second washing stepwherein the material is washed with pure water; and (e) drying thematerial.
 14. The method as recited in claim 13, wherein a concentrationof the surfactant in the aqueous solution is in the range of 150 ppm to5000 ppm.
 15. The method as recited in claim 14, wherein the aqueoussolution has a temperature of less than 100°.
 16. The method as recitedin claim 13, wherein a concentration of the surfactant in the aqueoussolution is in the range of 450 to 3000 ppm.
 17. The method as recitedin claim 13, wherein the surfactant is selected from the groupconsisting of hydrocarbon surfactants having a C₁₂ -C₁₈ hydrophobicalkyl group, and hydrophobic silicon surfactants.
 18. The method asrecited in claim 13, wherein the drying step occurs in a reducedpressure atmosphere.
 19. The method as recited in claim 13, wherein thedrying step occurs using a hot gas blow.
 20. The method according toclaim 13, wherein the first washing step occurs for 10 seconds or more.21. The method as recited in claim 13, wherein the drying step iscarried out using steam having a temperature ≦100°.
 22. The method asrecited in claim 13, wherein the first washing step occurs from 30seconds to 2 minutes.